1. Field of the Invention
The present invention relates to a printing press and more particularly a structure of a printing section disposed between a sheet feeding section and a sheet discharge section so as to supply a printing plate to a clamping gripper that is mounted on a plate cylinder and mount the same on the plate cylinder.
2. Related Art
A sheet-fed printing press (hereinafter referred simply to a printing press) generally includes a printing section between a sheet feeding section and a sheet discharge section. This printing section is to print on sheets by a printing plate mounted on a plate cylinder. The printing press is generally equipped with a printing plate mounting device that automatically mounts a printing plate, which has been manually inserted into a clamping gripper mounted on the plate cylinder. According to a recently proposed printing press, an automatic supply mechanism is employed to automatically supply a printing plate (a new plate), which has been once set at a predetermined position by an operator, to a clamping gripper.
Also, there is another type of a printing press equipped with a plate discharge device that discharges a printing plate (used plate) in a plate discharge direction after the finish of the printing operation. For example, Japanese Patent No. 2844231 proposes a plate discharge device, in which a printing plate is held at a trailing edge in engagement with a plate hook within a loader; this plate hook is connected to a blade spring wound around a convex so that the printing plate is pulled out in the plate discharge direction by a spring restoring force of the blade spring. In this plate discharge device, the plate hook is disposed so as to be pivotally moved around a support shaft so as to be urged against a guide wall of the loader by a coil spring, taking an upright position when not in a plate discharge operation. When in a plate discharging operation, a separately provided cylinder device is driven so as to allow its rod to press the plate hook that is in turn pivotally moved away from the guide wall to take a tilting position, forming a space with respect to the guide wall, into which a trailing edge of the printing plate is insertable. As the plate cylinder rotates, the trailing edge of the printing plate is inserted between the plate hook and the guide wall. Then, the plate hook is pivotally moved to again take the upright position by releasing pressure of the cylinder device therefrom, allowing the trailing edge of the printing plate to be held by the plate hook. At this moment, the printing plate is interposed between the plate hook and the guide wall so that the plate hook no longer engages with the guide wall and hence is pulled out in the plate discharge direction by a spring force of the blade spring. In this device, it is possible to pull out a printing plate by a sufficient distance in the plate discharge direction, depending on the distance between the convex and the position at which the plate hook is mounted.
According to the above conventional plate discharge device of the printing press, it is possible to pull out a printing plate by a sufficient distance in the plate discharge direction. However, this plate discharge device, which has the convex with the blade spring wound therearound, the plate hook, the coil spring for holding the plate hook in the upright position, a cylinder device for pressing the plate hook, and a means for allowing the plate hook to be urged against the guide wall, causes the entire device to have a complicated structure. In order to address this problem, it may be conceivable to provide a relatively simple structure with rollers for clamping the trailing edge of a printing plate, in which these rollers are moved in the plate discharge direction by the use of a cylinder device, thus achieving the discharge of the printing plate. However, in order to move the printing plate in the plate discharge direction by a sufficient distance, it is necessary to provide a cylinder device having a long stroke, which may lead to increase in the entire size of the device. Increase in the entire size of the device poses a problem to close the downstream side of an ink fountain provided adjacent thereto, and hence deteriorate the performance to operate the ink fountain such as in feeding ink, cleaning and maintenance operations.
It is an object of the present invention to provide a printing press that is capable of pulling out a printing plate in the plate discharge direction by a sufficient length while limiting the increase of the entire size of the plate discharge device.